Swede midge unconfirmed in the Northern Great Plains
Swede midge was not detected in canola grown in the Northern Great Plains between 2006 and 2021. Monitoring continues in North Dakota and western Canada to ensure early detection of swede midge if it continues to move northwestwards.
The swede midge, Contarinia nasturtii (Kieffer) is an invasive insect pest in North America with host plants including brassicaceous weeds, vegetables, and field crops, including canola.
Swede midge was first confirmed in North America in Ontario, Canada in the early 2000s, and is now established in Québec, Prince Edward Island, and Nova Scotia. In the United States, swede midge was first confirmed in New York State in 2004, and is now detected in New Jersey, Connecticut, Massachusetts, Vermont, Ohio, Michigan, Maine, New Hampshire, Illinois, Pennsylvania, and Minnesota.
Economic damage has been reported in many of these regions, and yield losses in canola have reached more than 50% in Ontario. As a result, canola acreage in Ontario has decreased.
In the spring, overwintered larvae pupate and the adult swede midge emerge from the soil. These adults are small brown flies less than 2 mm and are difficult to identify at this stage. Females lay eggs into the growing points of host plants and the hatched larvae feed on developing plant tissue for 7 to 21 days. The larvae are 3 to 4 mm in size and are clear to yellow coloured maggots. Larval feeding causes canola racemes and florets to become deformed or aborted. Mature larvae ‘jump’ to the soil to pupate, and either emerge as adults in 14 days, or enter diapause to overwinter.
In 2003 in Saskatchewan, unknown dipteran larvae ‘jumping’ from canola pods were reported. Because swede midge was spreading in eastern Canada, researchers on the Canadian Prairies initiated a small-scale monitoring program using pheromone traps in 2006. In 2007 in Manitoba and 2008 in Saskatchewan, male swede midge were detected on traps by the Canadian Food Inspection Agency. The small-scale monitoring program in western Canada was scaled up following the CFIA detections. Monitoring began in North Dakota in 2016.
The swede midge pheromone trapping in western Canada from 2006 to 2011 used white Jackson traps baited with synthetic swede midge pheromone. Two to four traps were installed 40 to 50 m apart along field edges from time of bolting to swathing. The sticky trap liners were replaced approximately weekly, and the traps were replaced every six weeks. Ninety-five per cent of sites included canola with the remaining other cruciferous vegetables.
The trap liners were sent to the Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada (Saskatoon, Saskatchewan) to determine if external morphology matched that of swede midge.
From 2006 to 2011, swede midge were not identified at any of the western Canadian locations, and monitoring was discontinued in 2012. But after suspected larval damage was observed in Saskatchewan fields, it was resumed in 2013 with the same protocol.
The trap sites were spread across Manitoba, Saskatchewan, Alberta and the Peace region of British Columbia. The number of traps varied per year, but totalled 521 sites from 2013 to 2021.
The distribution of sites where pheromone traps were deployed between 2006 and 2021 to monitor for the presence of Contarinia nasturtii (swede midge) across the canola-producing region (yellow-shaded area of the map) of the Northern Great Plains.
The monitoring programme in western Canada was supported by volunteers and collaborators, including farmers, professional agronomists, provincial agronomists and entomologists, industry commission staff, and researchers from Agriculture and Agri-Food Canada and prairie universities.
In North Dakota, a total of 117 trap sites were established between 2015 and 2021. Sites were primarily in canola with 10% in cruciferous garden crops in locations in the primary canola-producing areas, including the northeast and north–central areas near the Canadian–American border.
No news is good news
Adult swede midge has not been detected in pheromone traps across western Canada and North Dakota between 2006 and 2021. Additionally, no crop damage caused by swede midge has been observed during this time period.
The monitoring programme indicates that the swede midge has not established reproductive populations in this region. This is likely because the insect pest has not been introduced in sufficient numbers and that abiotic conditions are not favourable for swede midge development or reproduction.
However, swede midge remains a potential threat to canola production in western Canada and North Dakota. Monitoring remains a key tool in detection of emerging swede midge populations. The swede midge monitoring programme in western Canada is currently overseen by the Prairie Pest Monitoring Network and its many provincial, industrial, and academic collaborators.
The authors note that they continued the monitoring programme in 2022 through 2024, with between 40 to 60 fields per year in the BC Peace River region, AB, SK, and MB. No swede midge were found in traps in 2022 or 2023. The 2024 traps are being processed with results expected in January 2025. Hopefully, no news is still good news.
The Prairie Pest Monitoring Network plans to maintain the annual pheromone-based monitoring programme for swede midge as part of its annual survey and monitoring activities in field crops.
The swede midge monitoring program in western Canada was financially supported by two Canola Agronomic Research Program (CARP) grants, CARP 2017-12 and CARP 2017-13, and by the funding partners of the Integrated Crop Agronomy Cluster (Activity 2, supporting the Prairie Pest Monitoring Network) through the AgriScience Program as part of the Canadian Agricultural Partnership, a federal, provincial, and territorial initiative. Financial support was provided to Boyd Mori by a Natural Sciences and Engineering Research Council of Canada Industrial Research Chair (Grant 545088) and partner organisations, the Alberta Wheat Commission, the Alberta Barley Commission, the Alberta Canola Producers Commission, and the Alberta Pulse Growers Commission during the preparation of the manuscript.
Vankosky MA, Hladun S, Williams J, et al. Pheromone trap monitoring reveals the continued absence of swede midge in the Northern Great Plains. The Canadian Entomologist. 2023;155:e7. doi:10.4039/tce.2022.38
Photo by Jon Williams (AAFC Saskatoon)
Adult midge sitting on a canola growing point where larvae are developing – with larvae
